Cannabinoid was discovered as the main active substance contained in marijuana in 1960 and found to exhibit an activity in the central nervous system (illusion, euphoria, sensory confusion of time and space) and in the peripheral cell system (immunosuppressive activity, anti-inflammatory activity, analgesic activity).
After that, anandamide and 2-arachidonoylglycerol produced from arachidonic acid-containing phospholipids were discovered as endogenous agonists to the cannabinoid receptor. These endogenous agonists are known to exhibit an activity to the central nervous system and an activity to the peripheral cell system. It is disclosed in Hypertension (1997) 29, 1204-1210 that anandamide exhibits an activity to the cardiovascular system.
A cannabinoid type 1 receptor discovered in 1990 was found to be distributed over the central nervous system such as the brain. Agonists to this receptor were found to suppress the release of neurotransmitters to cause central actions such as analgesic effect or illusion. A cannabinoid type 2 receptor discovered in 1993 was found to be distributed over immune tissues such as the spleen. Agonists to this receptor were found to suppress an activation of immunocyte or inflammatory cells to exhibit an immunosuppressive activity, an anti-inflammatory activity and an analgesic activity (Nature, 1993, 365, 61-65).
Therefore, antagonists or agonists to the cannabinoid type 2 receptor are expected as immunosuppressive agents, anti-inflammatory agents, and analgesic agents (Nature, 1998, 349, 277-281).
In WO99/02499 and WO00/40562, described as a compound having an antagonistic activity or an agonistic activity to the cannabinoid type 2 receptor are quinolone derivatives. These quinolone derivatives are the compounds having a benzene ring substituted with dialkoxy and a nitrogen atom of the quinolone ring substituted with a hydrogen atom or methyl as shown below. 
On the other hand, disclosed in EP0481802 and J. Med. Chem. 1998, 36, 953-066 are pyridone derivatives having anti-HIV activity.
Furthermore, disclosed in Japanese Patent Publication Kokai 1983-46068 is a quinolone derivative represented by (A) as an intermediate of medicament, and in J. Chem. Soc. Perkin. Trans. I (1984), p1173-1182 discloses a pyridone derivative represented by (B). 